It is known from published patent specification GB.2,262,139 to apply a permanent load to the radially inner ends of an assembly of fan blades on a disk. It is achieved by cranked rods, one end portion of each of which is inserted in the space between the bottom of each respective groove and the radially inner end of the associated blade, in engagement with both, and the other end of which projects from the groove and is acted upon by a force ring. The latter is clamped via an inner flange to the disk, and the clamping force causes the ring to spread in the radial sense. An outer lip thus presses on the outer end of the cranked rod, which pivots about its inner end portion in a radially outwards direction, and thereby applies the required permanent force to the radially inner end of each blade.